Among the naturally occurring tetraborate ores, relatively few are ubiquitous, thus commercially valuable. As examples, there may be mentioned tincal or borax (Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O), kernite or rasorite (Na.sub.2 B.sub.4 O.sub.7.4H.sub.2 O), tincalconite (Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O), and the most common refined tetraborates, such as borax pentahydrate (Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O) and anhydrous borax (Na.sub.2 B.sub.4 O.sub.7). These are given as illustrative examples of boron-containing minerals which may be employed in the practice of the present invention, but it is to be understood that the invention is in no way intended to be limited thereto. In fact, this invention is quite versatile and is designed to utilize any of the tetraborate ores and refined tetraborates for manufacturing ammoniumtriborate and ammoniumpentaborate.
If the tetraborate ore is calcined to render it anhydrous prior to treatment, methylborate-ammonia adduct [(CH.sub.3 O).sub.3 B.NH.sub.3 ] is produced which can be further processed into ammoniumpentaborate, as described in my co-pending application, Ser. No. 135,177, filed Mar. 28, 1980, and in my U.S. Pat. No. 4,196,177, issued Apr. 1, 1980.
A quantitative esterification of boric acid to methylborate in the presence of sulfuric acid has been earlier demonstrated by H. I. Schlesinger, H. C. Brown, D. L. Mayfield and J. R. Gilbreath, J. Am. Chem. Soc., 75, 213-215 (1953). Several patents dealt with the recovery of boron content from ores through the formation and distillation of the volatile methylborate (R. P. Calvert et al, U.S. Pat. No. 1,308,577, 1919; F. H. May et al, U.S Pat. No. 2,833,623, 1958).
Addition compounds between methylborate, ammonia and amines have been described by Goubeau et al, (Z. anorg. u. allgem. Chem. 266, 27-37, 1951; ibid, 266, 161-174, 1951). H. A. Lehmann and W. Schmidt (Z. Chem. 5, 65-66 and 111, 1965) have described ammoniumpentaborate formation from boric acid and ammonia in polar solvents. But, the methylborate-ammonia adduct has not been prepared directly from alkali metal borates, such as tincal (borax) or other tetraborate ores.
As is also mentioned above, the commercially important ammonium pentaborate can be produced in accordance with the present invention. Ammoniumpentaborate was previously manufactured exclusively from the less abundantly occurring alkaline earth pentaborates, such as colemanite, Gerstley borate (e.g., U.S. Pat. No. 3,103,412; Swiss Pat. No. 354,760; Belgian Pat. No. 631,217; Italian Pat. No. 794,945) and potassiumpentaborate (e.g., U.S. Pat. No. 2,948,592). Transformation of borax to ammoniumpentaborate in dilute (10%) aqueous ammoniumchloride solution at 100.degree. C. was earlier reported (U.S. Pat. No. 2,867,502; Ch. O. Wilson et al, Advances in Chem., Serial No. 32, 20-26, 1961). In these processes, the separation of sodiumchloride and ammoniumpentaborate was cumbersome. Most importantly, the distillation of a large volume of water from the pentaborate required high energy. As will subsequently be described, the process according to the present invention, which uses different reagents and solvent, requires significantly lower energy.
As a sole product, ammoniumtetraborate (biborate of ammonia) was obtained from alkali metal or alkaline earth metal borate ores upon the treatment of their water suspension with ammoniumcarbonate, ammoniumhydrocarbonate, ammoniumsulfite or ammoniumbisulfite (Ch. Masson et al, Brit. Pat. No. 10,361, 1897). But, in the absence of methanol, no ammoniumtriborate (NH.sub.4.B.sub.3 O.sub.5.3CH.sub.3 --OH) could be formed.